A turbomachine rotor typically comprises a plurality of blades, a rotor axis and a rotor disc. A blade typically comprises an aerofoil, a platform and a root. A blade is also called a rotor blade or a rotor blade assembly. The root of the blade is used for joining the blade and the rotor disc and making sure that the blade is fixed to the rotor disc in both idle state and operating mode of the turbomachine.
There exist different ways for joining the blade and the rotor disc. One way is the provision of mounting grooves or slots in a radially outward section of the rotor disc. The root of the blade is inserted, e.g. slid in the slot. By choosing a shape of the root that corresponds to the shape of the slot, a secure and resilient joint can be achieved.
It is known to use a firtree shape for the profile of the root of the rotor blade and the corresponding slot of the rotor disc. Such a profile provides an accurate placement of the blade with respect to the rotor disc. Furthermore, firtree profiles are relatively strong to withstand the radially outward, i.e. centrifugal, forces imposed on the blade during rotation of the rotor disc together with its attached blades. However, after a certain lifetime of the root, the root may break due to the stress and the mechanical load, particularly at sections that are in physical contact with the slot surfaces in the rotor disc. Alternatively, there may also be damages and breakage at the slot surfaces or the adjacent sections of the rotor disc, particularly again at or near these sections that are in physical contact with the root of the rotor blade.
Thus there exists the goal to optimise the distribution of the stress and the mechanical load across the root and across the slot surfaces. More specifically, the distribution of the stress and the mechanical load across the contact faces between the root and the slot shall be optimised.